U.S. patent application number 12/408130 was filed with the patent office on 2009-09-24 for one-piece double balance spring and method of manufacturing the same.
This patent application is currently assigned to NIVAROX-FAR S.A.. Invention is credited to Pierre-Andre Buhler, Thierry Conus, Pierre Cusin, Jean-Bernard Peters, Jean-Phillipe Thiebaud, Marco Verardo.
Application Number | 20090236782 12/408130 |
Document ID | / |
Family ID | 39884625 |
Filed Date | 2009-09-24 |
United States Patent
Application |
20090236782 |
Kind Code |
A1 |
Buhler; Pierre-Andre ; et
al. |
September 24, 2009 |
ONE-PIECE DOUBLE BALANCE SPRING AND METHOD OF MANUFACTURING THE
SAME
Abstract
The invention relates to a double balance spring (21) including,
made in a layer of silicon-based material (11), a first balance
spring (23) coaxially mounted on a collet (13, 27), the collet (13,
27) including an extending part (9) that projects from said balance
spring and which is made in a second layer of silicon-based
material (5). According to the invention, said extending part
extends (17) into a third layer (7) of silicon-based material
coaxially with a second balance spring (25) so as to form a
one-piece double balance spring (21) made of silicon-based
materials. The invention also relates to a timepiece including a
balance spring of this type and the method of manufacturing the
same. The invention concerns the field of timepiece movements.
Inventors: |
Buhler; Pierre-Andre;
(Orvin, CH) ; Verardo; Marco; (Les Bois, CH)
; Conus; Thierry; (Lengnau, CH) ; Thiebaud;
Jean-Phillipe; (Cudrefin, CH) ; Peters;
Jean-Bernard; (La Chaux-de-Fonds, CH) ; Cusin;
Pierre; (Villars-Burquin, CH) |
Correspondence
Address: |
GRIFFIN & SZIPL, PC
SUITE PH-1, 2300 NINTH STREET, SOUTH
ARLINGTON
VA
22204
US
|
Assignee: |
NIVAROX-FAR S.A.
Le Locle
CH
|
Family ID: |
39884625 |
Appl. No.: |
12/408130 |
Filed: |
March 20, 2009 |
Current U.S.
Class: |
267/85 ;
29/896.9 |
Current CPC
Class: |
G04B 17/066 20130101;
Y10T 29/49609 20150115; G04D 3/0041 20130101 |
Class at
Publication: |
267/85 ;
29/896.9 |
International
Class: |
F16F 1/40 20060101
F16F001/40; B23P 13/00 20060101 B23P013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 20, 2008 |
EP |
08153094.1 |
Claims
1. A double balance spring, which comprises, made in a layer of
silicon-based material, a first balance spring coaxially mounted on
a collet, wherein the collet includes one extending part projecting
from said balance spring, which is made in a second layer of
silicon-based material, said extending part extending into a third
layer of silicon-based material coaxial with a second balance
spring to form a one-piece double balance spring made of
silicon-based materials.
2. The double balance spring according to claim 1, wherein the
collet has approximately the same section in each of said layers so
as to facilitate adjustment of said double balance spring.
3. The double balance spring according to claim 1, wherein the
collet has a substantially different section across at least one of
the layers.
4. The double balance spring according to claim 1, wherein the
balance springs include coils wound in the same direction.
5. The double balance spring according to claim 1, wherein the
balance springs include coils wound in different directions.
6. The double balance spring according to claim 1, wherein the ends
of the outer curves of each of the balance springs are plumb with
each other to allow single means to be used for pinning said double
balance spring up to the collet.
7. The double balance spring according to claim 1, wherein the
balance springs have the same angular stiffness.
8. The double balance spring according to claim 1, wherein the
balance springs each have distinct angular stiffness.
9. The double balance spring according to claim 1, wherein at least
one of the balance springs has at least one silicon dioxide-based
part so as to make said balance spring more mechanically resistant
and to adjust the thermo-elastic coefficient thereof.
10. The double balance spring according to claim 1, wherein the
inner coil of at least one of the balance springs has a Grossmann
curve so as to improve the concentric development of said double
balance spring.
11. The double balance spring according to claim 1, wherein the
collet has one metal part for receiving an arbour that is driven
therein.
12. A timepiece wherein it includes a double balance spring
according to claim 1.
13. A method of manufacturing a double balance spring including the
following steps: a) Providing a substrate including a top layer and
a bottom layer of silicon-based materials, b) selectively etching
at least one cavity in the top layer to define the pattern of a
first part of a collet, made of silicon-based material, of said
double balance spring, wherein it further includes the following
steps: c) joining an additional layer of silicon-based material to
the etched top layer of the substrate, d) selectively etching at
least one cavity in the additional layer to continue the pattern of
the collet and to define the pattern of a first balance spring,
made of silicon-based material, of said double balance spring, e)
selectively etching at least one cavity in the bottom layer to
continue the pattern of the collet and to define the pattern of a
second balance spring, made of silicon-based material, of said
double balance spring, and f) releasing the double balance spring
from the substrate.
14. The method according to claim 13, wherein, after step d), it
further includes the following step: g) oxidising the first balance
spring, made of silicon-based material, so as to make said balance
spring more mechanically resistant and to adjust the thermo-elastic
coefficient thereof.
15. The method according to claim 13, wherein, after step e), it
further includes the following step: g') oxidising the second
balance spring, made of silicon-based material, so as to make said
balance spring more mechanically resistant and to adjust the
thermo-elastic coefficient thereof.
16. The manufacturing method according to claim 13, wherein, prior
to step e), it further includes the following step: h) selectively
depositing at least one metal layer on the bottom layer to define
the pattern of a metal part on the collet.
17. The manufacturing method according to claim 16, wherein step h)
includes the following phase: i) growing said deposition by
successive metal layers at least partially over the surface of the
bottom layer so as to form the metal part for receiving an arbour
that is driven therein.
18. The manufacturing method according to claim 16, wherein step h)
includes the following phases: j) selectively etching at least one
cavity in the bottom layer for receiving the metal part; k) growing
said deposition by successive metal layers at least partially in
said at least one cavity so as to form the metal part for receiving
an arbour, which is driven therein.
19. The manufacturing method according to claim 16, wherein step h)
includes the following last phase: l) polishing the metal
deposition.
20. The manufacturing method according to claim 13, wherein several
double balance springs are made on the same substrate.
Description
FIELD OF THE INVENTION
[0001] The invention concerns a double balance spring and the
method of manufacturing the same and, more specifically, a double
balance spring formed in a single piece.
BACKGROUND OF THE INVENTION
[0002] The regulating member of a timepiece generally includes an
inertia wheel, called a balance, and a resonator called a balance
spring. These parts have a determining role as regards the working
quality of the timepiece. Indeed, they regulate the movement, i.e.
they control the frequency of the movement.
[0003] In the case of a double balance spring, materials have been
tested in order to limit the influence of a temperature change on
the regulating member in which it is integrated, without resolving
difficulties regarding assembly or resonance adjustment.
SUMMARY OF THE INVENTION
[0004] It is an object of the present invention to overcome all or
part of the aforecited drawbacks, by providing a double, one-piece
balance spring whose thermo-elastic coefficient can be adjusted and
which is obtained using a manufacturing method that minimises
assembly difficulties.
[0005] The invention therefore concerns a double balance spring
that includes, made in a layer of silicon-based material, a first
balance spring coaxially mounted on a collet, the collet including
one extending portion that projects from said balance spring and
which is made in a second layer of silicon-based material,
characterized in that said extending portion extends into a third
layer of silicon-based material coaxially with a second balance
spring in order to form a one-piece, double balance spring made of
silicon-based materials.
[0006] According to other advantageous features of the invention:
[0007] the collet has approximately the same section in each of
said layers so as to facilitate adjustment of said double balance
spring; [0008] the collet has an approximately different section
over at least one of the layers, [0009] the balance springs include
coils that wind in the same direction or pitch, [0010] the ends of
the outer curves of each of the balance springs are plumb with each
other so that single means can be used for pinning said double
balance spring up to the collet, [0011] the balance springs have
the same angular stiffness or pitch, [0012] at least one of the
balance springs has at least one part made of silicon dioxide to
make it more mechanically resistant and to adjust its
thermo-elastic coefficient, [0013] the inner coil of at least one
of the balance springs has a Grossmann curve so as to improve the
concentric development of said coil, [0014] the collet has a metal
part into which an arbour is driven.
[0015] More generally, the invention relates to a timepiece,
characterized in that it includes a double balance spring in
accordance with any of the preceding variants.
[0016] Finally, the invention relates to a method of manufacturing
a double balance spring that includes the following steps: [0017]
a) providing a substrate including a top layer and a bottom layer
of silicon-based materials, [0018] b) selectively etching at least
one cavity in the top layer to define the pattern of a first part
of a collet, made of silicon-based material, of said double balance
spring, [0019] c) joining an additional layer of silicon-based
material to the etched top layer of the substrate, [0020] d)
selectively etching at least one cavity in the additional layer to
continue the pattern of the collet and to define the pattern of a
first balance spring, made of silicon-based material, of said
double balance spring, characterized in that it further includes
the following steps: [0021] selectively etching at least one cavity
in the bottom layer to continue the pattern of the collet and to
define the pattern of a second balance spring, made of
silicon-based material, of said double balance spring, [0022]
releasing the double balance spring from the substrate.
[0023] According to other advantageous features of the invention:
[0024] after step d), it includes step g): oxidising the first
balance spring made of silicon-based material so as to make it more
mechanically resistant and to adjust its thermo-elastic
coefficient, [0025] after step e), it includes step g'): oxidising
the second balance spring made of silicon-based material so as to
make it more mechanically resistant and to adjust its
thermo-elastic coefficient, [0026] prior to step e), it includes
step h): selectively depositing at least one metal layer on the
bottom layer to define the pattern of a metal part on the collet,
[0027] step h) includes step i): growing said deposition by
successive metal layers at least partially over the surface of the
bottom layer, so as to form the metal part for receiving an arbour,
which is driven therein, [0028] step h) includes steps j):
selectively etching at least one cavity in the bottom layer for
receiving the metal part and step k): growing said deposition by
successive metal layers at least partially in said at least one
cavity so as to form the metal part into which an arbour will be
driven, [0029] step h) includes a last step l): polishing the metal
deposition, [0030] several double balance springs are made on the
same substrate, which allows batch manufacture.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] Other peculiarities and features will appear more clearly
from the following description, which is given by way of
non-limiting illustration, with reference to the annexed drawings,
in which:
[0032] FIGS. 1 to 5 show successive view of the manufacturing
method according to the invention,
[0033] FIGS. 6 to 8 show views of the successive steps of
alternative embodiments,
[0034] FIG. 9 shows a flow chart of the method according to the
invention,
[0035] FIGS. 10 and 11 are perspective diagrams of a one-piece,
double balance spring according to a first embodiment.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0036] The invention relates to a method, generally designated 1,
for manufacturing a double balance spring 21 for a timepiece
movement. As illustrated in FIGS. 1 to 9, method 1 includes
successive steps for forming at least one type of one-piece, double
balance spring, which can be entirely formed of silicon-based
materials.
[0037] With reference to FIGS. 1 and 9, the first step 100 consists
in providing a silicon-on-insulator (SOI) substrate 3. Substrate 3
includes a top layer 5 and a bottom layer 7 each formed of
silicon-based material.
[0038] Preferably, in this step 100, substrate 3 is selected such
that the height of bottom layer 7 matches the height of one part of
the final double balance spring 21.
[0039] Preferably, top layer 5 is used as spacing means relative to
bottom layer 7. Consequently, the height of top layer 5 will be
adapted in accordance with the configuration double balance spring
21. Depending upon said configuration, the thickness of top layer 5
may thus fluctuate, for example, between 10 and 200 .mu.m.
[0040] In a second step 101, seen in FIG. 2, cavities 8 and 10 are
selectively etched, for example by a DRIE (deep reactive ionic
etch) process, in top layer 5 of silicon-based material. These
cavities 8 and 10 can preferably form a pattern 9 that defines the
inner and outer contours of one part of the collet, made of
silicon-based material, of the double balance spring.
[0041] In the example illustrated in FIGS. 10 and 11, pattern 9
forms the median part of collet 27 of double balance spring 21. As
FIG. 2 illustrates, pattern 9 is approximately cylinder-shaped with
a circular section. However, advantageously according to method 1,
the etch on the top layer 5 leaves complete freedom as regards the
geometry of pattern 9. Thus, it might not necessarily be circular,
but, for example, elliptical and/or have a non-circular inner
diameter.
[0042] In a third step 102, shown in FIG. 3, an additional layer 11
of silicon-based material is added to substrate 3. Preferably,
additional layer 11 is secured to top layer 5 by means of silicon
fusion bonding (SFB). Thus, step 102 advantageously covers top
layer 5 by binding the top face of pattern 9, with a very high
level of adherence, to the bottom face of additional layer 11.
Additional layer 11 may, for example, have a similar thickness to
that of bottom layer 7.
[0043] In a fourth step 103, shown in FIG. 4, cavities 12 and 14
are selectively etched, for example, by a DRIE process similar to
that of step 101, in additional silicon layer 11. These cavities 12
and 14 form two patterns 13 and 15, which define the inner and
outer contours of the silicon parts of double balance spring
21.
[0044] In the example illustrated in FIG. 4, pattern 13 is
approximately cylindrical with a circular section, and pattern 15,
is approximately spiral-shaped. However, advantageously according
to method 1, the etch on additional layer 11 allows complete
freedom for the geometry of patterns 13 and 15. Thus, in
particular, pattern 15 may, for example, include more coils or an
open outer curve.
[0045] Preferably, pattern 13 made in additional layer 11 is of
similar shape and plumb with pattern 9 made in top layer 5. This
means that cavities 10 and 12, respectively forming the inner
diameter of patterns 9 and 13, communicate with each other and are
substantially one on top of the other. In the example illustrated
in FIGS. 10 and 11, patterns 13 and 9 respectively form the upper
and median parts of collet 27 of double balance spring 21.
[0046] Preferably, at least one bridge of material 16 is formed to
hold double balance spring 21 on substrate 3 during manufacture. In
the example illustrated in FIG. 4, it can be seen that a bridge of
material 16 is left between the outer curve of pattern 15 and the
rest of the non-etched layer 11.
[0047] Advantageously, as patterns 13 and 15 are etched at the same
time, they form a one-piece part in additional layer 11. In the
example illustrated in FIGS. 10 and 11, patterns 13 and 15 form
respectively the top part of collet 27 and the first balance spring
23 of double balance spring 21.
[0048] After this fourth step 103, it is clear that patterns 13 and
15 etched in additional layer 11 are connected by the bottom of
pattern 13, with a high level of adherence, above pattern 9, which
is etched in top layer 5 and laterally, by the outer curve of
pattern 15, to additional layer 11.
[0049] Preferably, as shown in dotted lines in FIG. 9, method 1 can
include a fifth step 104 that consists in oxidising at least
pattern 15, i.e. the first balance spring 23 of the double balance
spring so as to make said first balance spring more mechanically
resistant and to adjust its thermo-elastic coefficient. This
oxidising step is explained in EP Patent No. 1 422 436, which is
incorporated herein by reference.
[0050] Advantageously, according to the invention, after fourth
step 103, or preferably, after fifth step 104, method 1 may include
three embodiments A, B and C, as illustrated in FIG. 9. However,
each of the three embodiments A, B and C ends in the same final
step 106, which consists in releasing the manufactured double
balance spring 21 from substrate 3.
[0051] Advantageously, release step 106 can be achieved simply by
applying sufficient force to double balance spring 21 to break
bridges of material 16. This force may, for example, be generated
manually by an operator or by machining.
[0052] According to a first embodiment A, in a sixth step 105,
shown in FIG. 5, cavities 18 and 20 are selectively etched, for
example by a similar DRIE process to that of steps 101 and 103, in
bottom layer 7 of silicon-based material. These cavities 18 and 20
form two patterns 17 and 19, which define the inner and outer
contours of silicon parts of double balance spring 21.
[0053] In the example illustrated in FIG. 5, pattern 17 is
approximately cylinder-shaped with a circular section and pattern
19 is approximately spiral-shaped. However, advantageously
according to method 1, the etch in bottom layer 7 leaves complete
freedom as to the geometry of patterns 17 and 19. Thus, in
particular, pattern 19 may, for example, have more coils or an open
outer curve.
[0054] Preferably, pattern 17, made in bottom layer 7, is of
similar shape and substantially plumb with pattern 9 made in top
layer 5. This means that cavities 18, 10 and 12 respectively
forming the inner diameters of patterns 17, 9 and 13, communicate
with each other and are approximately one on top of the other. In
the example illustrated in FIGS. 10 and 11, patterns 13, 9 and 17
form the one-piece collet 27 of double balance spring 21.
[0055] Preferably, at least a second bridge of material 16 is
formed to hold double balance spring 21 on substrate 3 during
manufacture. The example illustrated in FIG. 5 shows that one
bridge of material 16 is left between the outer curve of pattern 19
and the rest of the non-etched layer 7.
[0056] Advantageously, as patterns 17 and 19 are etched at the same
time, they form a one-piece part in bottom layer 7. In the example
illustrated in FIGS. 10 and 11, patterns 17 and 19 form
respectively the bottom part of collet 27 and the second balance
spring 25 of double balance spring 21.
[0057] After this sixth step 105, it is clear that patterns 17 and
19 etched in bottom layer 7 are connected by the top of pattern 17,
with a high level of adherence, above pattern 9, which is etched in
top layer 5 and, laterally, by the outer curve of pattern 19 to
bottom layer 7.
[0058] After final step 106, explained above, first embodiment A
thus produces a one-piece double balance spring 21, formed entirely
of silicon-based materials, as shown in FIGS. 10 and 11. It is thus
clear that there are no longer any assembly problems, since
assembly is performed directly during manufacture of double balance
spring 21. The latter includes a first balance spring 23 and a
second balance spring 25, which are joined coaxially to each other
by a single collet 27.
[0059] As explained above, collet 27 is formed by the three
successive patterns 13, 9 and 17 by etching the successive
respective layers 11, 5 and 7. It is thus clear that median pattern
9 is useful as spacing means between the first balance spring 23
and the second balance spring 25, but also as guide means for said
balance springs. Advantageously, according method 1, it is thus
possible, via the choice of thickness of top layer 5, to define
directly the space between the two balance springs 23 and 25 and
the guide quality thereof.
[0060] Similarly, the height of balances springs 23, 25 and,
incidentally, those of top and bottom parts 13 and 17 of collet 27,
which are not necessarily equal, can be directly defined by the
choice of thickness of additional layer 11 and bottom layer 7.
[0061] Moreover, the etches carried out in steps 103 and 105 of
method 1 allow complete freedom as to the geometry of balance
springs 23, 25 and collet 27. Thus, in particular, each balance
spring 23 and 25 can have its own number of coils, its own
geometrical features in proximity to collet 27, its own coil
winding direction and also its own curve geometry, particularly as
regards the external part. By way of example, one and/or the other
of balance springs 23, 25 can thus have an open outer curve so as
to cooperate with an index assembly or have, on the end of the
outer curve, a bulge portion that can be used as a point of
attachment.
[0062] In accordance with the same reasoning, collet 27 can have
uniformly peculiar or different dimensions and/or geometries at
least over one of bottom 17, median 9 and/or top 13 parts. Indeed,
depending upon the arbour on which collet 27 will be mounted, the
inner diameter can have a complementary shape over all or part of
the height of collet 27. Likewise, the inner and/or outer diameters
are not necessarily circular but may be, for example, elliptical
and/or polygonal.
[0063] In the example illustrated in FIGS. 10 and 11, balance
springs 23 and 25 have the same height, i.e. they are etched in
layers 7 and 11 of the same thickness and they have the same number
of coils. The ends of their outer curve are shifted relative to the
collet by an angle of approximately 180.degree.. Finally, the coils
of balance springs 23 and 25 have opposite winding directions.
Moreover, collet 27 is of entirely uniform height and it is
approximately cylinder-shaped with a circular section.
[0064] As explained above, because of the manufacturing freedom
allowed by method 1, things could be different, i.e. the ends of
the outer curve of each balance spring 23, 25 could be plumb with
each other which would advantageously enable single means to be
used for pinning the two balance springs 23 and 25 up to the
collet.
[0065] It should also be noted that the very good structural
precision of deep reactive ionic etching decreases the start radius
of each of balance springs 23 and 25, i.e. the external diameter of
collet 27, which means that the internal and external diameters of
collet 27 can be miniaturised. It is thus clear that double balance
spring 21 can advantageously receive, via its cavities 18, 10 and
12, an arbour of smaller diameter than is currently usually
manufactured.
[0066] Preferably, said arbour can be secured to the internal
diameter 18 and/or 10 and/or 12 of collet 27. Tightening can be
achieved using resilient means etched in silicon collet 27. Such
resilient means may, for example, take the form of those disclosed
in FIGS. 10A to 10E of EP Patent No. 1 655 642 or those disclosed
in FIGS. 1, 3 and 5 of EP Patent No. 1 584 994, said Patents being
incorporated herein by reference.
[0067] According to a second embodiment B, after step 103 or 104,
method 1 includes a sixth step 107, shown in FIG. 6, consisting in
implementing a LIGA process (from the German "rontgenLlthographie,
Galvanoformung & Abformung"). This process includes a series of
steps for electroplating a metal on the bottom layer 7 of substrate
3 in a particular shape, using a photostructured resin. As this
LIGA process is well known, it will not be described in more detail
here. Preferably, the metal deposited may be, for example, gold or
nickel or an alloy of these metals.
[0068] In the example illustrated in FIG. 6, step 107 may consist
in depositing a cylinder 29. In the example illustrated in FIG. 6,
the cylinder 29 is for receiving an arbour, which is advantageously
driven therein. Indeed, one drawback of silicon is that it has very
few elastic and plastic zones, making it very brittle. The
invention thus proposes to fit an arbour, for example a balance
staff, not against the silicon of collet 27, but to the inner
diameter 28 of metal cylinder 29, which is electroplated during
step 107.
[0069] Advantageously, according to method 1, the cylinder 29
obtained by electroplating allows complete freedom as regards its
geometry. Thus, in particular, the inner diameter 28 is not
necessarily circular, but for example polygonal, which could
improve the transmission of stress in rotation with an arbour of
matching shape.
[0070] In a seventh step 108, similar to step 105 shown in FIG. 5,
cavities are selectively etched, for example by a DRIE method, in
bottom layer 7 of silicon-based material. These cavities allow
patterns to be formed for a second balance spring and a collet
similar to patterns 19 and 17 of the first embodiment A.
[0071] After final step 106, explained above, the second embodiment
B thus produces a one-piece, double balance spring formed of
silicon-based materials with the same advantages as embodiment A,
with the addition of a metal part 29. It is thus clear that there
is no longer any assembly problem since assembly is carried out
directly during manufacture of the double balance spring. Finally,
advantageously, an arbour can be driven against the inner diameter
28 of metal part 29. One could therefore envisage cavities 10 and
12 including sections of larger dimensions than that of inner
diameter 28 of metal part 29, so as to prevent the arbour being in
push fit contact with collet 27.
[0072] According to a third embodiment C, after step 103 or 104,
method 1 includes a sixth step 109 shown in FIG. 7, consisting in
selectively etching a cavity 30, for example, by a DRIE process, to
a limited depth in bottom layer 7 of silicon-based material. Cavity
30 forms a recess to be used as a container for a metal part. As in
the example illustrated in FIG. 7, the cavity 30 obtained can take
the form of a disc. However, advantageously according to method 1,
the etch of bottom layer 7 allows complete freedom as to the
geometry of cavity 30.
[0073] In a seventh step 110, as illustrated in FIG. 8, method 1
includes implementation of a galvanic growth or LIGA process for
filling cavity 30 in accordance with a particular metal shape.
Preferably, the deposited metal may be, for example, gold or
nickel.
[0074] In the example illustrated in FIG. 8, step 110 may consist
in depositing a cylinder 31 in cavity 30. Cylinder 31 is for
receiving an arbour, which is advantageously driven therein.
Indeed, as explained above, one advantageous feature of the
invention consists in tightening the arbour, for example the
balance staff, not against the silicon-based material of collet 27,
but on the inner diameter 32 of metal cylinder 31, which is
electroplated during step 110.
[0075] Advantageously according to method 1, cylinder 31 obtained
by electroplating allows complete freedom as to its geometry. Thus,
in particular, the inner diameter 32 is not necessarily circular
but, for example, polygonal, which could improve the transmission
of stress in rotation with an arbour of matching shape.
[0076] Preferably, method 1 includes an eighth step 111, consisting
in polishing the metal deposition 31 made during step 110, in order
to make said deposition flat.
[0077] In a ninth step 112, similar to step 105 shown in FIG. 5,
cavities are selectively etched, for example, by a DRIE process, in
bottom layer 7 of silicon-based material. These cavities form
patterns of a second balance spring and a collet similar to
patterns 19 and 17 of the first embodiment A.
[0078] After final step 106 explained above, third embodiment C
produces a one-piece, double balance spring formed of silicon-based
materials with the same advantages as embodiment A, with the
addition of a metal part 31. It is thus clear that there are no
longer any assembly problems, since assembly is carried out
directly during manufacture of the double balance spring. Finally,
advantageously, an arbour can be driven against inner diameter 32
of the metal part. One could therefore preferably envisage cavities
10 and 12 including sections of larger dimensions than that of the
inner diameter 32 of metal part 31, to prevent the arbour being in
push fit contact with collet 27.
[0079] According to the three embodiments A, B and C, it should be
understood that the final double balance spring 21 is thus
assembled prior to being structured, i.e. prior to being etched
and/or altered by electroplating. This advantageously minimises the
dispersions generated by current assemblies of two balance springs
and, consequently, improves the precision of a regulator member on
which it will depend.
[0080] Advantageously, according to the invention, it is also clear
that it is possible for several double balance springs 21 to be
made on the same substrate 3, which allows batch production.
[0081] Moreover, it is possible to make a driving insert of the
same type as metal depositions 29 and/or 31 also, or solely from
additional layer 11 and/or top layer 5. One could also envisage the
two balance springs 23 and 25 being oxidised to make them more
mechanically resistant and to adjust their thermo-elastic
coefficient. A conductive layer could also be deposited on at least
one part of double balance spring 21 to prevent isochronism
problems. This layer may be of the type disclosed in EP Patent No.
1 837 722, which is incorporated herein by reference. Finally, a
polishing step like step 111 may also be carried out between step
107 and step 108 as shown in dotted lines in FIG. 9.
* * * * *